Method of increasing rate of dissolution of aluminum in acid chloride solutions

ABSTRACT

A METHOD OF INCREASING THE RATE OF DISSOLUTION OF ALUMINUM IN ACID CHLORIDE SOLUTION WHICH COMPRISES THE STEPS OF ALLOYING THE ALUMINUM WITH FROM 0.04 TO 0.5% OF TIN AND THEN IMMERSING THE RESULTANT ALLOY INTO THE ACID SOLUTION.

United states Patent Ser. No. 12,491

Int. Cl. C01f 7/56 US. C]. 23-92 3 Claims ABSTRACT OF THE DISCLOSURE A method of increasing the rate of dissolution of aluminum in acid chloride solutions which comprises the steps of alloying the aluminum with from 0.04 to 0.5% of tin and then immersing the resultant alloy into the acid solution.

This application is a divisional of copending application Ser. No. 655,997, filed July 26, 1967, now abandoned.

It has been found that aluminum alloys containing 0.04 to 0.5 tin have increased dissolution rates in acid chloride solutions.

It is known in the art to manufacture aluminum chloride by dissolving aluminum powder in an acid aluminum chloride solution. However, eiforts have been made to substitute less expensive aluminum pig for aluminum powder as a source material. These efforts have not been successful because of slow and variable dissolution rates.

It is an object of this invention to provide an aluminum alloy which has a rapid dissolution rate in acid chloride solutions.

It is another object of this invention to provide an aluminum alloy which has a rapid dissolution rate in acid chloride solutions even where the surface to volume ratio of said alloy is low.

It is another object of this invention to provide an aluminum alloy which has a relatively constant and predictable dissolution rate in acid chloride solutions.

It is still another object of this invention to provide an aluminum alloy in which said alloy in pig form may be substituted for aluminum powder of conventional composition for dissolution in acid aluminum chloride solution.

According to the present invention, it has been found that aluminum alloys containing from .04 to .5 Sn have rapid dissolution rates in acid aluminum chloride solutions.

The impurity limits of the aluminum-tin alloys of the present invention are:

Percent Sn 0.040.5 Fe, up to .2 Si, up to .15 Cu, up to .1 Mang, up to .1 Mg, up to .1 Zn, up to .1 All other impurities, each up to .1 Total impurities other than Sn 1.

The preferred tin content is from 0.06 to 0.25% because in this range the dissolution rate is relatively constant and 3,595,608 Patented July 27, 1971 ice,

predictable, which is desirable for commercial operation charging schedules.

The solutions used in dissolving the aluminum must contain chloride ions (generally from HCl but not limited thereto) and some water. Chloride salts yielding acid chloride solutions can be a part of or all of the dissolving solution. The pH of the solution must be maintained in the l to 7 range, but is generally from 1 to 5, as dissolution is more rapid in the higher acidic range. There is also generally present some aluminum ions present in the solution from previously dissolved metallic aluminum. However, if desired, the dissolution process can be successfully begun with no aluminum ions present in the dissolving solutions.

A further advantageous feature of the present invention is that no complicated or expensive treatments are required to prepare the alloys for dissolution. Conventional melting and casting techniques, well known to those skiled in the art, can thus be practiced.

Thus, for example, grade 6A or other high purity aluminum may be melted in conventional melting facilities made, for instance, of clay and/or graphite. The melting temperature can be, for instance, from 1250 to 1350 F. The Sn can be added to the thus melted metal.

It is desirable to degas the molten alloy just before casting, for example, with chlorine gas. Conventional molds can be used for casting.

The following exampes illustrate the invention without limiting its scope.

EXAMPLE I The metals used in these examples are based on grade 6A aluminum (i.e. 99.85% +pure aluminum). In some instances, grade 6A has been alloyed with high purity tin.

For samples A, B and C small, approximately 12 gram, buttons of 6A aluminum were made by casting molten aluminum into a constant size iron chill mold treated with a lime wash. In all cases the specimen weight and surface area was constant.

For samples D through H, the aluminum charges were melted in a clay-graphite crucible. When the melt was fully liquified it was fluxed with gaseous chlorine for a period of 2 minutes at a temperature of 1315 F., the melts being stirred for 4 minutes after introduction of the amount of tin specified in D through H, before casting into the chill mold as described above.

TABLE I Samples of the following compositions were prepared by the method outlined above.

Tin .001

B Silicon .06 Iron .09 Copper .00l Chromium .001 Nickel .001 Zinc .001 Tin a- .001 Titanium .00l Boron .001 Manganese .006 Magnesium .001 Vanadium .002 Gallium .013 Sodium .004

C Silicon .06 Iron .07 Copper .00l Chromium .0O1 Nickel .001 Zinc .00l Tin .00l Titanium .001 Boron .001 Manganese .006 Magnesium .001 Vanadium .001 Gallium .013 Sodium .004

D Iron .05 Tin .08 Silicon .04 Boron .003 Gallium .013 Copper .001 Chromium .001 Nickel .001 Zinc .001 Titanium .00l Manganese .001 Magnesium .001 Vanadium .001 Gallium .001 Sodium .001

E Silicon .09 Iron .11 Tin .08 Chromium .00l Nickel .001 Zinc .0O1 Titanium .001 Boron .001 Manganese .008 Magnesium .002 Vanadium .00l Gallium .013 Copper .002

F Silicon .09 Iron .11 Tin .08 Copper a .002 Chromium .00l Nickel .00l Zinc .00l Titanium .00l Boron .00l Manganese .008 Vanadium .0O1 Gallium .013 Magnesium .002

4 G Silicon .04 Copper .002 Manganese .004 Chromium .002 Zinc .01 Magnesium .00l Iron .08 Titanium .004 Boron .004 Gallium .015 Tin .11 Bismuth .16

H (Al0.2% Sn) Silicon .04 Copper .002 Manganese .004 Chromium .002 Zinc .01 Magnesium .001 Iron .06 Titanium .004 Boron .002 Gallium .015 Tin .22

EXAMPLE 2 Duplicate samples of each of the foregoing alloys with constant mass and with constant ratio of surface area to volume were reacted with an equal portion of the same acid aluminum chloride solution. Reaction was conducted until such a time as each sample had dissolved completely in the electrolyte.

The average dissolution rates were computed from the mass dissolved and the time taken for complete dissolution. The results were expressed on a basis relative to the dissolution rate of a comparable mass of mesh 6A aluminum powder having composition essentially identical to Composition A. The dissolution rate of the powdered sample (having a much higher ratio of surface area to volume) was taken as unity and all other dissolution rates given in Table II are shown on a proportionate basis to this sample.

TABLE II The following dissolution rates were found for the various samples in the acid aluminum chloride solution.

Sample: Dissolution rate (A) 100 mesh powder 1.0 (A) Chill casting .31 (B) Chill casting .30 (C) Chill casting .59 (D) Chill casting 1.89 (E) Chill casting 1.77 (F) Chill casting 1.92 (G) Chill casting 1.59 (H) Chill casting 1.68

It can be seen from Table II that a reduction in the surface area to volume ratio in pure aluminum leads to a reduction in dissolution rate. Furthermore, essentially pure aluminum chill castings of almost identical composition give widely differing dissolution rates.

The aluminum-tin alloys of the present invention, by contrast, show enhanced dissolution rates relative to pure aluminum powder, despite a reduction in surface area to volume ratio.

It is to be understood that the invention is not limited to the illustrations described and shown herein which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modifications of form, size, arrangement of parts and detail of operation, but rather is intended to encompass all such modifications which are within the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A method of increasing the rate of dissolution of aluminum in acid chloride solutions comprising alloying with said aluminum from 0.04% to 0.5% tin and then inserting the thus formed alloy into the acid solution.

2. A process according to claim 1 in which the amount of tin added is from 0.06% to 0.25%

3. A process according to claim 1 in which an aluminum chloride solution is obtained by reaction of the aluminum with said acid chloride solutions.

6 References Cited FOREIGN PATENTS 6/1938 Australia 23-92 OTHER REFERENCES 10 EDWARD STERN, Primary Examiner US. Cl. X.R. 23-154; 75-138 

